Police said they were investigating the arrested man's relationship with other foreigners in the Genoa area to determine whether they were trying to recruit fighters.

The man's brother and three Libyans were among those being investigated, and several mosques or Islamic cultural centers in Genoa and the city of Rapallo about 28 kilometers (17.4 miles) away had been searched, police sources said.

In Rome, new security plans include stationing police at entry points to the Colosseum amphitheatre and extending an existing "maximum security zone" around St. Peter's Basilica at the Vatican.

In an apparent response to last week's murder of a priest in a French church, Rome increased surveillance of religious sites around the city, the police commissioner said in a statement.

Authorities will also inspect shopping centers to prepare contingency plans, an apparent reaction to the shooting dead of nine people in a Munich mall last month.

Rome police will also step up checks on cruise ship passengers and night clubs, and "clean up" illegal settlements along the banks of the Tiber river.

On Tuesday, Interior Minister Angelino Alfano said Italy had expelled a 26-year-old Pakistani man who authorities said supported Islamic State and was planning to go to Syria to join Islamist militants.

(Reporting by Philip Pullella; Additional reporting by Isla Binnie in Rome and Lisa Barrington in Beirut; Editing by Tom Heneghan)